Regular editing on MediaWiki blocks edits from browsers that do not support basic unicode characters. Although it's unlikely that any browser will run into that problem, we should think about mirroring that behavior.

See https://gerrit.wikimedia.org/r/#/c/374422/ and T67297

The EditPage does block an edit after it was submitted by showing a warning to the user: It appears that your browser does not support Unicode. It is required to edit pages, so your edit was not saved.

For us it would be also possible to block edits beforehand showing a warning on the page where you can change the text / title. In any case users could still import files but would just have no option to edit the text or title.